《专业英语》-Unit5教学材料

Lesson14TheUseofMultimeterKeywordsmultimeter万用表physically物理地mode模式probe探测display显示屏upperlight高亮nominal额定的over-range超量程drift漂流下一页返回Lesson14TheUseofMultimeterHowtodetectwhetherthekey“w”andthekey“e”arephysicallyconnectedwithamultimeter(seeFig14-1)Afteradeepconsideration,wewillfindtheproblemisequaltotheproblemofdeterminingcontinuityoftwopointsinPCBwithmultimeter.Inordertoachievethetask,wemaytrythesestepsasfollowing下一页上一页返回Lesson14TheUseofMultimeterGetintothemodeFirststepistogetyourmultimeterintothecorrectmode.Lookfortheiconthatlookssortoflikea“soundwave”.Herearetwoexamples.Notethatsometimesthemodeis“dual”(orpossiblymore)usage,asshowninFig14-2

下一页上一页返回Lesson14TheUseofMultimeterTouchandgo

Foramajorityofmultimeters,you’rereadytogo,justtouchthetipsoftheprobestogethersothattheymakeabeepingsound!HerearesomeexamplescoveringacoupleofdifferentmultimetersExample1:Thismeterisverysimple.Whentheprobesarenottouching,thedisplayshows“1”Whenyoutouchthetipstogether,thedisplaychangestoathreedigitmode(it’sdisplayingresistance,whichwewillcoverlater).Italsoemitsabeep,asshowninFig14-3下一页上一页返回Lesson14TheUseofMultimeterExample2:Thismeterisdualmodebutstillveryeasytouse.Turnthedialtothesymbol.Whentheprobesarenottouchingthedisplayshows“OL”whichstandsforOpenLoop.Whenyoutouchtheprobes,thesoundwaveiconshowsupinthedisplay(upperright)anditalsoshowsanumber.Thenumberisnottheresistance,actuallyit’sthevoltageasshowninFig14-4

下一页上一页返回Lesson14TheUseofMultimeterProbingaPCBExample:HereisanexampleoftestingaPCBforcontinuity.Thefirsttestshowsthatthetwopointsarenotconnected;thesecondtestshowsthatthesetwopointsareconnected,asshowninFig14-5

下一页上一页返回Lesson14TheUseofMultimeterHowtomeasurethevoltageofdailybatterieswithamultimeter?Voltagetestingisverycommon,you’lluseitalot.Beforeyourtestinacircuit,youmustmakesurethecircuitispowered,andvoltageisalwaysmeasuredbetweentwopoints,inaddition,itisdirectional下一页上一页返回Lesson14TheUseofMultimeterGetintotherightmodeThereareoftentwoseperatemodesforACandDCvoltage.BothwillhaveaVbutonewillhavetwolines,onedashedandonesolid(DC)andonewillhaveawavenexttoit(AC),asshowninFig14-6

AsshowninFig14-6:thismeterhasthedoublelineforDCvoltage,and5ranges,from200mVto600V.Thelightningboltsymbolisagentlereminderthatthisvoltageisextremelydangerous下一页上一页返回Lesson14TheUseofMultimeterVoltagetestingExample1:Thefirstbatterywe’lltestisanew1.5Valkalineone.ThisoneisaAAAbutaAA,CorDcellwillbethesamevoltage.Settherangeto2VDCAsshowninFig14-7,weread1.588V,whichyoumaythinkisamistake,afterallit’sa1.5Vbatterysoshouldn’titbe1.5V?Notquite,the1.5Vwrittenonthesideisjustanominalvoltage,orthe“average”youmayexpectfromthebattery.Inreality,analkalinebatterystartsouthigher,andthenslowlydriftsdownto1.3Vandthenfinallyto1.0Vandevenlower下一页上一页返回Lesson14TheUseofMultimeterExample2:Wemeasurea9Valkalinebattery.Ifwestillhavetherangesetto2VDC,wewillgetamysterious“1”display,indicatingitisover-range,asshowninFig14-8

Fixtherangesothatit’s20V,andtryagainForthisnewbatteryweget9.6V.Rememberthatbatteryvoltageisnominal,whichmeansthatthe“9V”isjusttheaveragevoltageofthebattery.Inreality,itstartsoutashighas9.5Vandthendropsdownto9Vandthenslowlydriftsto7VMultimeterisveryuseful,itcandoresistancetesting,besidescontinuitytestingandvoltagetesting上一页返回Lesson15OscilloscopeKeywordsradio收音机input庶入output庶出coupling藕合component元件sensitivity灵敏度button旋钮scan扫描automatic自动measure测量cable电缆下一页返回Lesson15OscilloscopeHowtocalculatethefrequencydifferenceofaudiosignalsandoutputsignalsofradiousingtheoscilloscope?AsshowninFig15-1

Inordertowatchthefrequencydistortionoftwosignals，wegenerateamodulatedsignalwhichisa1kHzaudiosignalwiththecarrywavefrequencyof88MHzfromsignalgeneratorasaninputsignal，throughtheradio，andgettheoutputsignal.Themaintaskistosimultaneouslydisplaytwowaves,andfindthedifferenceofaudiosignalsandoutputsignalsToachievethegoal,youmaytrythefollowingsteps下一页上一页返回Lesson15OscilloscopeTurnonthepower

AsshowninFig15-2,the“Power”buttonisusedtoturntheoscilloscopeonandoff.Arealoscilloscopeneedsawarmuptimebeforeitcandisplayasignalonthescreen下一页上一页返回Lesson15OscilloscopeCheckandadjustbeforeusingoscilloscopesItisnecessarytomakeappropriateadjustmentforyourfirstusingoscilloscopesSelectcouplingmodeUsingthe“DC/AC/GD”switches,theinputcouplingofachannelcanbeselectedInposition“AC”(=alternatingcurrentcoupling)thesignalisRCcoupled.ItsDCcomponentisfiltered.Inposition“DC”(=directcurrentcoupling)theDCcomponentsarenotfiltered.Here，wechoosethe“AC”mode,asshowninFig15-3

下一页上一页返回Lesson15OscilloscopeSelectsensitivityofYaxisAsshowninFig15-4,the“Volts/Div”wheelsamplifyaninputsignalsothatforadivisionagivenvoltagelevelisinvalid.A“Division”isasegment,asquareonthescreenoftheoscilloscope.The“Volts/Div”wheelismadeupoftwowheels.Thebiggerwheelisusedforacoarseadjustmenttocalibratedvalues.Toobtaincalibratedvalues,thesmallerwheelmustbesettoitsleftmostposition.Usingthesmallerwheellocatedontopofthebigwheelafineadjustmentcanbemade.Thesmallwheelhoweveriscalibratedforitsleftmostpositiononly,asshowninFig15-5andFig15-6

下一页上一页返回Lesson15OscilloscopeSelectthesourceoftriggeringsignalsandpolarityAsshowninFig15-7,the“+/-”buttondetermineswhetherasignalistriggeredonascendingflank(+)ordescendingflank(-).Ifthebuttonisoff,theascendingflankisused，otherwisethedescendingflankisused.Thissettingisindependentfrommanualorautomatictriggerlevelsetting下一页上一页返回Lesson15OscilloscopeSelectscanningspeedAsshowninFig15-8,the“Time/Div”wheeldetermines,howlongtheelectronicbeamwhichdrawsthecurveneedsformovingfromthelefttotherightedgeofadivision.Thewheelcontrolsthe“Timescale”.A“Division”isonesquareonthescreenoftheoscilloscope.The“Time/Div”wheelismadeupoftwowheels,asshowninFig15-9andFig15-10

下一页上一页返回Lesson15OscilloscopeInputmeasuredsignalAsshowninFig15-11,fourcablescoloredpurple,blue,greenandorangearelocatedatthelowerscreenborderuponsimulationstart.Theycanbedraggedontoasignalinputconnectoroftheoscilloscopeusingthemouseandengageautomaticallyoncethemousebuttonislifted.UsingthesametechniqueacablecanbedetachedfromaninputconnectorbydraganddropHere，becausewewanttocomparetheinputandoutputsignals,wetakethe“Dual”mode.Wechoosech2asthemodulatedsignalandch1astheoutputsignal,asshowninFig15-12下一页上一页返回Lesson15OscilloscopeAsanalternative,“Chop”modecanbeusedtodisplaytwosignalsonthescreen.Chopmodeisonwhenboth,the“Dual”buttonandthe“Add”buttonarepressedHere，becauseofwejustcaretheoutputsignals，weonlypayattentiontofrequencyofch1’ssignals.Inordertofastcalculatingthefrequency，weshouldconfigureYpositionandsensitivityExample1：ChoosethesameYpositiontomakesurethewavesareatthesamereferenceline,asshowninFig15-13

下一页上一页返回Lesson15OscilloscopeExample2：ToappropriatelyadapttheXpositiontomakesuregridsareatthestartingpointoftheperiod,soastoaccuratelycalculatethefrequencyoftheoutputsignals,asshowninFig15-14

Then,wewillgetthewaveslikethis,asshowninFig15-15Finally，wewillcalculatethefrequencydifferenceofaudiosignalsandoutputsignals下一页上一页返回Lesson15OscilloscopeDefinitely，ifyouthinktheimageisnotclear,youcouldachieveitthroughadjustingthe“Focus”.The“Focus”isusedtosetthefocusoftheelectronicbeam.Whenyouturnthewheel,thefocusmaybeoutofposition(infrontoforbehindthedisplayplane)andtheimagewillbeblurred,asshowninFig15-16

上一页返回Lesson16SignalGeneratorKeywordsconfigure配置parameter参数modulate调制carrier载波instantanous瞬间的amplitude幅度transmission传愉channel调制下一页返回Lesson16SignalGeneratorConfigureawaveof700MHzand-20dBmwithN5181A/82AMXG,asshowninFig16-1Toachievethetask，IthinkthefollowingstepswilldoPresetthesignalgenerator

Toreturnthesignalgeneratortoaknownstate,presseitherPresetorUserPreset,asshowninFig16-2.Presetisthefactorypreset;UserPresetisacustompreset.Toresetpersistentsettings(thoseunaffectedbypreset,userpreset,orpowercycle),Press:Utility>PowerOn/Preset>RestoreSystemDefaults.下一页上一页返回Lesson16SignalGeneratorWealsoshouldcaution：Toavoidthelossofdata,GPIBsettings,orcurrentuserinstrumentstatesthathavenotbeenpermanentlysavedtonon-volatilememory,theMXGshouldalwaysbepowereddowneitherviatheMXG’sfrontpanelpowerbuttonortheappropriateSCPIcommand.MXG’sinstalledinracksystemsandpowereddownwiththesystemrackpowerswitchratherthantheMXG’sfrontpanelswitchdisplayaError-310duetotheMXGnotbeingpowereddowncorrectly,asshowninFig16-3

下一页上一页返回Lesson16SignalGeneratorSetRFfrequencyPressFreq>700>MHzstepbystep,asshowninFig16-4

InFrequencymode,thismenuisautomaticallydisplayedwhenenteringanumericvaluewiththefrontpanelkeypad,asshowninFig16-5

下一页上一页返回Lesson16SignalGeneratorSettheRFamplitudePressAmptd>-20>dBmstepbystep,asshowninFig16-6

InAmplitudemode,thismenuisautomaticallydisplayedwhenenteringanumericvaluewiththefrontpanelkeypad,asshowninFig16-7

下一页上一页返回Lesson16SignalGeneratorTurnontheRFOutputPressRFOn/Off，theRFoutputLEDlights,indicatingthatthesignalistransmittingfromtheRFoutputconnector,asshowninFig16-8

下一页上一页返回Lesson16SignalGeneratorGenerateanAMsignalAmplitudemodulation(AM)isamethodofimpressingdataontoacarrierwaveform,asshowninFig16-9.Thehighestfrequencyofthemodulatingdataisnormallylessthan10percentofthecarrierfrequency.Theinstantaneousamplitude(overallsignalpower)variesdependingontheinstantaneousamplitudeofthemodulatingdata下一页上一页返回Lesson16SignalGeneratorPresetthesignalgeneratorAsshowninFig16-10

SetthecarrierfrequencyAsshowninFig16-11

Thetransmissionofafixedfrequencythathasbeenaltered(modulated)to“carry”data.ThefrequencyismeasuredinHertz下一页上一页返回Lesson16SignalGeneratorAwaveformwhichhasafixedcenterfrequencyisusedtocontaindataandestablishauniquechannelthatcanbeidentifiedindependentlyofotherchannels.Carriersaretheprimarymethodusedtosendwirelesssignalsthroughtheairinordertodifferentiatetransmittingstations.Forexample,AMandFMradio,TV,satelliteandWi-Fiallusecarriers.Infact,AMandFMradioactuallyusethecarrierfrequencyastheirstation’schannelnumber下一页上一页返回Lesson16SignalGeneratorSettheRFamplitudeAsshowninFig16-12

ConfigurethemodulationPressAMSettheAMtype(LinearorExponential):AMTypetohighlightdesiredtypeSettheAMMode(NormalorDeep).DefaultisDeep.ToselectNormalenable.MoretohighlightdesiredtypeSettheAMDepth:AMDepth>value（Default0.01%andrange0.01%to100%）.Settherate:AMRate>value>frequencyunit,asshowninFig16-13

下一页上一页返回Lesson16SignalGeneratorTurnonthemodulationAsshowninFig16-14

PressAM>AMOff/On,asshowninFig16-15

Commonmodulationmethodsinclude:Amplitudemodulation(AM),inwhichthevoltageappliedtothecarrierisvariedovertimeFrequencymodulation(FM),inwhichthefrequencyofthecarrierwaveformisvariedinsmallbutmeaningfulamountsPhasemodulation(PM),inwhichthenaturalflowofthealternatingcurrentwaveformisdelayedtemporarily下一页上一页返回Lesson16SignalGeneratorTurnontheRFoutputTheRFoutputLEDlights,indicatingthatthesignalistransmittingfromtheRFoutputconnector下一页上一页返回Lesson16SignalGeneratorConfiguringasweptoutputThesignalgeneratorispowerfulItcannotonlygeneratecontinuouswavesandmodulatedsignals，butalsoachievesweepingoutputSetupeitherastepsweep(page52)oralistsweep(page58).IntheSweep/Listmenu,selectaparametertosweep:PressSweep>parameter>ReturnSelectmanualmode:PressMore>ManualModeOff/On.Whenyouselectmanualmode,thecurrentsweeppointbecomestheselectedmanualpoint.下一页上一页返回Lesson16SignalGeneratorIfitisnotalreadyon,turntheRFoutputon:PressRFOn/OffSelectthedesiredpointtooutput:PressManualPoint>number>Enter.Theprogress